Declaration Order
-----------------
-Here is the order in which code should be laid out in a file:
+Here is the preferred order in which code should be laid out in a file:
- commented program name and one-line description
- commented author name and email address(es)
\s\s\s\sif (expr) {\n\tstmt; --ick.) The only exception to this rule is
multi-line comments that use an asterisk at the beginning of each line, i.e.:
- /t/*
- /t * This is a block comment.
- /t * Note that it has multiple lines
- /t * and that the beginning of each line has a tab plus a space
- /t * except for the opening '/*' line where the slash
- /t * is used instead of a space.
- /t */
+ \t/*
+ \t * This is a block comment.
+ \t * Note that it has multiple lines
+ \t * and that the beginning of each line has a tab plus a space
+ \t * except for the opening '/*' line where the slash
+ \t * is used instead of a space.
+ \t */
Furthermore, The preference is that tabs be set to display at four spaces
wide, but the beauty of using only tabs (and not spaces) at the beginning of
do {
+If you have long logic statements that need to be wrapped, then uncuddling
+the bracket to improve readability is allowed. Generally, this style makes
+it easier for reader to notice that 2nd and following lines are still
+inside 'if':
+
+ if (some_really_long_checks && some_other_really_long_checks
+ && some_more_really_long_checks
+ && even_more_of_long_checks
+ ) {
+ do_foo_now;
Spacing around Parentheses
~~~~~~~~~~~~~~~~~~~~~~~~~~
}
+Labels
+~~~~~~
+
+Labels should start at the beginning of the line, not indented to the block
+level (because they do not "belong" to block scope, only to whole function).
+
+ if (foo) {
+ stmt;
+ label:
+ stmt2;
+ stmt;
+ }
+
+(Putting label at position 1 prevents diff -p from confusing label for function
+name, but it's not a policy of busybox project to enforce such a minor detail).
+
+
Variable and Function Names
---------------------------
Exceptions:
- Enums, macros, and constant variables are occasionally written in all
- upper-case with words optionally seperatedy by underscores (i.e. FIFOTYPE,
+ upper-case with words optionally separated by underscores (i.e. FIFO_TYPE,
ISBLKDEV()).
- Nobody is going to get mad at you for using 'pvar' as the name of a
conversion.
- Compile and see if everything still works.
-
+
Please be aware of changes that have cascading effects into other files. For
example, if you're changing the name of something in, say utility.c, you
should probably run 'examples/mk2knr.pl utility.c' at first, but when you run
Don't do this:
- #define var 80
+ #define CONST 80
Do this instead, when the variable is in a header file and will be used in
- several source files:
+ several source files:
- const int var = 80;
+ enum { CONST = 80 };
- Or do this when the variable is used only in a single source file:
-
- static const int var = 80;
-
-Declaring variables as '[static] const' gives variables an actual type and
-makes the compiler do type checking for you; the preprocessor does _no_ type
-checking whatsoever, making it much more error prone. Declaring variables with
-'[static] const' also makes debugging programs much easier since the value of
-the variable can be easily queried and displayed.
+Although enum may look ugly to some people, it is better for code size.
+With "const int" compiler may fail to optimize it out and will reserve
+a real storage in rodata for it! (Hopefully, newer gcc will get better
+at it...). With "define", you have slight risk of polluting namespace
+(#define doesn't allow you to redefine the name in the inner scopes),
+and complex "define" are evaluated each time they uesd, not once
+at declarations like enums. Also, the preprocessor does _no_ type checking
+whatsoever, making it much more error prone.
The Folly of Macros
Code cluttered with ifdefs is difficult to read and maintain. Don't do it.
Instead, put your ifdefs at the top of your .c file (or in a header), and
conditionally define 'static inline' functions, (or *maybe* macros), which are
-used in the code.
+used in the code.
Don't do this:
(in .h header file)
- #ifdef CONFIG_FEATURE_FUNKY
- static inline void maybe_do_funky_stuff (int bar, int baz)
+ #if ENABLE_FEATURE_FUNKY
+ static inline void maybe_do_funky_stuff(int bar, int baz)
{
/* lotsa code in here */
}
#else
- static inline void maybe_do_funky_stuff (int bar, int baz) {}
+ static inline void maybe_do_funky_stuff(int bar, int baz) {}
#endif
(in the .c source file)
certain library functions are (mis)used. The following table offers a summary
of some of the more notorious troublemakers:
-function overflows preferred
-----------------------------------------
-strcpy dest string strncpy
-strcat dest string strncat
-gets string it gets fgets
-getwd buf string getcwd
-[v]sprintf str buffer [v]snprintf
-realpath path buffer use with pathconf
-[vf]scanf its arguments just avoid it
+function overflows preferred
+-------------------------------------------------
+strcpy dest string safe_strncpy
+strncpy may fail to 0-terminate dst safe_strncpy
+strcat dest string strncat
+gets string it gets fgets
+getwd buf string getcwd
+[v]sprintf str buffer [v]snprintf
+realpath path buffer use with pathconf
+[vf]scanf its arguments just avoid it
The above is by no means a complete list. Be careful out there.
Avoid Big Static Buffers
------------------------
-First, some background to put this discussion in context: Static buffers look
+First, some background to put this discussion in context: static buffers look
like this in code:
/* in a .c file outside any functions */
- static char *buffer[BUFSIZ]; /* happily used by any function in this file,
+ static char buffer[BUFSIZ]; /* happily used by any function in this file,
but ick! big! */
The problem with these is that any time any busybox app is run, you pay a
and the right thing will happen, based on your configuration.
+Another relatively new trick of similar nature is explained
+in keep_data_small.txt.
+
Miscellaneous Coding Guidelines
would be required, lots more memory would be used, etc.)
- The difference is minor or cosmetic
-A note on the 'cosmetic' case: Output differences might be considered
+A note on the 'cosmetic' case: output differences might be considered
cosmetic, but if the output is significant enough to break other scripts that
use the output, it should really be fixed.
if (foo)
stmt1;
new_line();
- stmt2
+ stmt2;
stmt3;
And the resulting behavior of your program would totally bewilder you. (Don't
Furthermore, you should put a single comment (not necessarily one line, just
one comment) before the block, rather than commenting each and every line.
-There is an optimal ammount of commenting that a program can have; you can
+There is an optimal amount of commenting that a program can have; you can
comment too much as well as too little.
A picture is really worth a thousand words here, the following example
illustrates how to emphasize logical blocks:
- while (line = get_line_from_file(fp)) {
+ while (line = xmalloc_fgets(fp)) {
/* eat the newline, if any */
chomp(line);
Processing Options with getopt
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-If your applet needs to process command-line switches, please use getopt() to
+If your applet needs to process command-line switches, please use getopt32() to
do so. Numerous examples can be seen in many of the existing applets, but
basically it boils down to two things: at the top of the .c file, have this
-line in the midst of your #includes:
+line in the midst of your #includes, if you need to parse long options:
#include <getopt.h>
+Then have long options defined:
+
+ static const struct option <applet>_long_options[] = {
+ { "list", 0, NULL, 't' },
+ { "extract", 0, NULL, 'x' },
+ { NULL, 0, NULL, 0 }
+ };
+
And a code block similar to the following near the top of your applet_main()
routine:
- while ((opt = getopt(argc, argv, "abc")) > 0) {
- switch (opt) {
- case 'a':
- do_a_opt = 1;
- break;
- case 'b':
- do_b_opt = 1;
- break;
- case 'c':
- do_c_opt = 1;
- break;
- default:
- show_usage(); /* in utility.c */
- }
- }
+ char *str_b;
+
+ opt_complementary = "cryptic_string";
+ applet_long_options = <applet>_long_options; /* if you have them */
+ opt = getopt32(argc, argv, "ab:c", &str_b);
+ if (opt & 1) {
+ handle_option_a();
+ }
+ if (opt & 2) {
+ handle_option_b(str_b);
+ }
+ if (opt & 4) {
+ handle_option_c();
+ }
If your applet takes no options (such as 'init'), there should be a line
somewhere in the file reads:
That way, when people go grepping to see which applets need to be converted to
use getopt, they won't get false positives.
-Additional Note: Do not use the getopt_long library function and do not try to
-hand-roll your own long option parsing. Busybox applets should only support
-short options. Explanations and examples of the short options should be
-documented in usage.h.
+For more info and examples, examine getopt32.c, tar.c, wget.c etc.